KR100928279B1 - Solid fuel combustion for industrial grade melting using slagging chamber - Google Patents

Abstract

The present invention relates to a method of supplying heat to a melting furnace to form a molten product using a ash containing fuel. The fuel with ash component is introduced into the slagging chamber of the slagging combustion furnace and burned at least partially with the first oxidant mixture and the second oxidant mixture in the slagging chamber. The ash component is collected as a layer of molten slag in the slagging chamber. The gaseous emissions of the slagging combustion furnace are transferred from the slagging chamber of the slagging combustion furnace to the combustion space of the hot melting furnace, supplying heat for forming the molten product. The molten slag is withdrawn from the slagging chamber of the slagging combustion furnace and is not selectively introduced into the furnace or introduced into the furnace.

Description

SOLID FUEL COMBUSTION FOR INDUSTRIAL MELTING WITH A SLAGGING COMBUSTOR}

FIELD OF THE INVENTION The present invention relates to the field of material melting and melting furnaces, and more particularly to melting materials by burning ash-containing fuel to supply heat during the melting process.

Gas and liquid fuels are commonly used to heat the furnace. The gas or liquid fuel is introduced into the furnace with the oxidant to form a combustion flame located above the molten product and / or input, which may be air, oxygen rich air, and / or industrial grade oxygen. The use of ash-containing solid fuels in the furnace is unusual because the ash component may cause defects in the molten product and the ash component may promote deterioration of the refractory material of the furnace.

In the prior art relating to supplying heat to a melting furnace using solid fuels, the solid fuel is reformed to use ash with a low ash content, use other furnace refractory materials, remove ash before burning the solid fuel, And operating the furnace to carry ash particles out of the furnace by air.

In Kobayashi's U.S. Patent Application 2006/0150677, which relates to reducing corrosion and particle emissions in glass melting furnaces, not only does the risk of ash in fuel being incorporated into the glass melt affecting the quality of the glass, but also fire resistance by ash deposition. To reduce the risk of material corrosion, fuels with low ash content are preferred. In general, the typical ash content of coal and petroleum coke is 5% to 20% and 0.1% to 1% by weight, respectively. Therefore, the preferred fuel in Kobayashi's process is petroleum coke.

In US Pat. No. 6,789,396 to Olin-Nunez et al. Concerning a method and system for supplying and burning fine fuel to a burner for the same purpose as a glass melting furnace, an object of the invention is to provide a method for burning and supplying fine fuel to a glass melting furnace and As a system, the method and system employing a special refractory material in the construction of a chamber of a glass melting furnace, with the aim of reducing the corrosion and abrasion action, in particular caused by V ₂ O ₅ , occurring through the combustion of the fine fuel. It is said to provide.

US Pat. No. 4,055,400 to Stambaugh et al., US Pat. No. 5,312,462 to Nowpak et al. And US Pat. No. 4,741,741 to Salem et al. Disclose methods for reducing the ash content of coal.

In US Pat. No. 4,006,003 to Daiga on the glass melting process, by maintaining a sufficient rate of ash flow left in the combustion of coal, residual ash can be kept suspended in the gas flow, resulting in ash content. It is found that ash is conveyed from the glass melting furnace out of a suitable port of this melting furnace by air, without being in contact with the glass melt or with any batch components carried on the surface of the glass melt. In this way, by adjusting the speed of the gas flow flowing over the surface of the glass melt, substantially all residual ash can be removed without coming into contact with the underlying melt pool.

It would be desirable to use ash containing fuels without causing unacceptable defects caused by ash.

It would be desirable to use a ash containing fuel without causing deterioration of the refractory material of the furnace which could not be tolerated.

The present disclosure relates to a method of supplying heat to a melting furnace to form a molten product. The method includes introducing a first fuel having ash and combustible components into a slagging chamber of a slagging combustion furnace; Introducing a first oxidant mixture having an oxygen concentration of 10 vol% to 100 vol%, 10 vol% to 20 vol%, or 20 vol% to 30 vol% into a slagging chamber of a slagging combustion furnace; Selectively introducing a second fuel into the slagging chamber of the slagging combustion furnace; Introducing a second oxidant mixture having an oxygen concentration of from 22% to 100%, from 60% to 75%, or from 85% to 100% by volume into a slagging chamber of the slagging furnace; Combusting at least a portion of the combustible components of the first fuel and at least a portion of the optional second fuel in a slagging chamber of the slagging furnace to form a separate ash component and form a gaseous emission to the slagging furnace; Collecting at least a portion of the separated ash component as a layer of molten slag in contact with at least a portion of an inner surface of the slagging chamber; Transferring at least a portion of the gaseous emissions of the slagging combustion furnace from the slagging chamber of the slagging combustion furnace to a combustion space in the furnace at a temperature of 1000 ° C. to 2500 ° C. to supply heat to form the molten product; And withdrawing molten slag from the slagging chamber of the slagging combustion furnace.

The gaseous emissions of the slagging combustion furnace may contain at least one unburned combustible gas. The method includes introducing a third oxidant mixture having an oxygen concentration of 20% to 100%, 60% to 75%, or 85% to 100% by volume into the combustion space of the furnace; And combusting at least a portion of the at least one unburned combustible gas obtained from the gaseous emissions of the slagging combustion furnace with the at least a portion of the third oxidant mixture in the combustion space of the furnace. The third oxidant mixture may be introduced between the gaseous emissions of the slagging combustion furnace and the melt / raw material space.

The first oxidant mixture may contain flue gas exiting the furnace, and the first oxidant mixture may have an oxygen concentration of 10% to 20% by volume.

The second fuel may contain at least a portion of the gaseous emissions of the slagging combustion furnace.

The method may further comprise introducing the molten slag into the furnace.

The melting furnace may be a glass melting furnace having a melting zone and a clarification zone. The method may further comprise introducing molten slag into the melting zone and not introducing it into the clarification zone.

The method may further comprise introducing a slagging additive into the slagging chamber. The slagging additive may comprise at least one of glass cullets, glassmaking raw materials, ash from other processes.

According to the present invention, the ash-containing fuel can be used for supplying heat to the melting furnace without causing a defect due to ash and without causing deterioration of the refractory material of the furnace.

The present invention relates to a method of supplying heat to a melting furnace to form a molten product. The method may include one or more of the features described below, that is, may take only one of the features or in any combination technically possible. An exemplary apparatus 1 for implementing this method is shown schematically in FIG. 1. The apparatus comprises a melting furnace 10 and a slagging combustion furnace 14.

For the sake of simplicity and clarity, the detailed description of well-known devices and methods is omitted to avoid obscuring the description of the present invention by what is unnecessarily detailed.

The furnace is any closed structure in which heat is generated to produce liquefied material from solid materials. In operation, the furnace usually has a combustion space 16 located above the melt / raw material space 18 that can accommodate the molten and unmelted material. The combustion space is a gaseous region located above the space that can accommodate molten and unmelted material and is mainly gaseous, bounded by the walls and roof of the furnace. Visible combustion flames are usually present in the combustion space, with the exception of the introduction of hot incombustible gases into the furnace to melt the material, or the use of combustion techniques that do not generate flames. Examples of melting furnaces include glass melting furnaces, copper melting furnaces and aluminum melting furnaces. Melting furnaces are well known. Construction materials and construction methods are known.

The molten product is any product that is melted or liquefied by heat. Examples of molten products are molten glass, molten copper and molten aluminum. The method of forming the melt product includes introducing heat as well as introducing the melt product forming material into the furnace.

The method includes introducing the first fuel 20 into the slagging chamber 12 of the slagging furnace 14. The first fuel has a ash component and a combustible component. The first fuel may be introduced directly into the slagging chamber or indirectly via an auxiliary burner conduit. The first fuel can be introduced together with the carrier gas (usually air). The first fuel is introduced at a first fuel flow rate F ₁ , the unit of which is for example kg / s or other suitable unit of measure. The first fuel has a first fuel total calorific value H ₁ , wherein the unit of the total calorific value is, for example, J / kg or another suitable unit of measure.

Fuel is a carbon-containing material used to produce heat or power by combustion. Examples of fuels are coal, petroleum coke (Pet coke), biofuels, heavy oil, diesel, gasoline, kerosene, propane, methane and natural gas.

The first fuel can be any fuel having a ash component and a combustible component. For example, the first fuel may be coal, petroleum coke, biofuel, or mixtures thereof.

The ash component is defined as any incombustible mineral that remains as a residue when the combustible material is completely oxidized or burned by chemical means. Ash contains inorganic incombustibles present in the parent fuel and usually contains oxides of silicon, aluminum, iron, calcium, magnesium, sodium, potassium and vanadium.

The combustible component is any substance capable of chemical exothermic reaction with oxygen.

A slagging combustion furnace is an apparatus for combusting at least a portion of a fuel having ash content with an oxidant, the apparatus comprising at least one conduit for introducing fuel and / or oxidant, at least one slagging chamber, and slag At least one discharge port for discharging gaseous emissions to the ging furnace. The molten slag may be discharged from at least one discharge port or through one or more other molten slag discharge ports or tabs.

The slagging chamber is any chamber or conduit comprised of a material compatible with molten slag, containing at least one fuel having a ash component, containing at least one oxidant mixture, and containing at least a portion of the ash component. It is defined as any chamber or conduit that collects as a layer of molten slag. Fuel having an ash component and an oxidant may be introduced into the slagging chamber and burned at least partially. The ash contained in the fuel can be heated to a temperature above the melting point of the ash, through which the ash is converted from the solid phase to the liquid phase or the molten phase. Molten ash (slag) is physically separated from the gaseous products of fuel combustion and collected as a layer of molten slag. Separation of the molten ash from the gas product in the slagging chamber may occur due to centrifugal force, inertial force, gravity, electrostatic force, magnetic force, other suitable forces, or a combination thereof.

The slagging chamber, which relies on centrifugal force, may be a cylindrical "barrel" in which the fuel with the ash component is introduced with significant tangential momentum, thereby accelerating the ash particles towards the walls of the chamber in which the slag layer is formed. This happens. The molten slag can flow towards the slag tab for discharge and removal by gravity.

Slagging chambers that depend on inertia and / or gravity may include "U" shaped conduits. Fuel having a ash component and an oxidant mixture may be introduced downward into the “U” conduit and combusted to form combustion products and separated ash components. The separated ash component may form a slag layer at the bottom of the “U” shaped conduit. The molten slag may be tapped at the bottom of the "U" conduit. Various geometries for separating the separated ash components from the combustion products by inertia and / or gravity can be easily devised.

The fuel (s) and oxidant (s) may be introduced horizontally into the gravity based slagging chamber having a horizontal section and a vertical section. The gas can flow upward in the vertical section, while the separated ash component moves downward after tapping the walls of the vertical section and taps at the bottom of the vertical section.

Those skilled in the art will readily be able to select a suitable slagging furnace with a slagging chamber. The particular form of the slagging chamber is not critical to the method of the present invention.

Slag chambers for boilers are known. For example, US Pat. Nos. 6,910,432 and 6,968,791 to D'Agostini et al., US Pat. No. 6,085,674 to Ashworth, US Pat. No. 5,878,700 to Farzan, and US Pat. No. 5,209,187 to Khinkis. See also.

The method includes the step of introducing the first oxidant mixture 22 into the slagging chamber of the slagging furnace. The first oxidant mixture is usually a gas and may have an oxygen concentration (Y ₁ ) of 10% to 100% by volume. The remainder of the first oxidant mixture may include species such as nitrogen and argon, etc., and may further include species such as carbon dioxide, sulfur dioxide and water vapor if recycle of flue gas is used, for example.

The first oxidant mixture may have an oxygen concentration of 20% to 30% by volume. The first oxidant mixture may be air.

Using recycle of flue gas, the first oxidant mixture may comprise flue gas exiting the melting furnace and may have an oxygen concentration of 10% to 20% by volume. The first oxidant mixture may be introduced directly into the slagging chamber as shown in FIG. 1 or may be introduced indirectly via an auxiliary burner conduit. The first oxidant mixture is introduced at a first oxidant mixture volume flow rate (V ₁ ).

The first oxidant mixture may be introduced in a tangential manner to cause centrifugal force, which causes the ash component separated from the first fuel to move towards the inner wall of the slagging chamber.

Optionally, the method includes introducing a second fuel 30 into a slagging chamber of a slagging combustion furnace. The second fuel may be a fuel that contains little ash component, i.e., less than 0.1% by weight. The second fuel may be heavy oil, diesel, gasoline, kerosene, propane, methane, natural gas, or a combination thereof. The second fuel may contain a portion of the gaseous emissions of the slagging combustion furnace. The second fuel may be provided to increase the temperature and combustion in the slagging chamber, thereby affecting the viscosity of the molten slag layer collected in the slagging chamber. If a second fuel is used, the second fuel is introduced at a second fuel flow rate F ₂ , the unit of which is for example kg / s or other suitable unit of measure. The second fuel has a second fuel total calorific value H ₂ , wherein the unit of the total calorific value is, for example, J / kg or another suitable unit of measure. If a second fuel is used, the second fuel can provide up to 25% of the total energy introduced into the slagging furnace, which is represented by the following equation.

The method includes introducing a second oxidant mixture 32 into the slagging chamber of a slagging furnace. The second oxidant mixture is usually a gas and may have an oxygen concentration (Y ₂ ) of 22 vol% to 100 vol%. The remainder of the second oxidant mixture may comprise nitrogen, carbon dioxide, water vapor, argon and traces of other species.

The second oxidant mixture may have an oxygen concentration of 60% to 75% by volume. An air separation plant producing nitrogen may have an oxygen discharge stream having an oxygen concentration of 60% to 75% by volume.

The second oxidant mixture may have an oxygen concentration of 85% by volume to 100% by volume. The second oxidant mixture may be industrial grade oxygen produced in an air separation plant.

As further described in US Pat. No. 6,968,791, a second oxidant mixture can be used to increase temperature and combustion in the slagging chamber, which can affect the viscosity of the molten slag layer collected in the slagging chamber. have. The second oxidant mixture is introduced at a second oxidant mixture volume flow rate (V ₂ ).

The method of the present invention combusts at least a portion of the combustible components of the first fuel and at least a portion of the second fuel (if present) in the slagging chamber of the slagging combustion furnace to form a separate ash component and generate the slag combustion furnace. Forming a gas discharge 40.

The separated ash component is any non-gas component that includes the ash component of the first fuel that has been separated from the combustible component during combustion.

The gas emissions from the slagging furnaces are any gas emissions from the slagging furnaces. The gaseous emissions of the slagging furnaces may contain combustion products and / or at least one unburned combustible gas.

Substantially all, such as at least 95% of the first fuel and all of the second fuel, may be combusted in a slagging furnace. Alternatively, a portion of the first fuel is combusted in a slagging combustion furnace, leaving at least one unburned combustible gas (also called incomplete combustion product), which is incompletely combusted in combustion in the furnace 10. It is available. If only a portion of the first fuel is combusted in the slagging combustion furnace, the gaseous emissions of the slagging combustion furnace will usually contain carbon monoxide as one of the unburned combustible gases.

The method includes collecting at least a portion of the separated ash component as a layer 44 of molten slag. The layer of molten slag may be formed in contact with at least a portion of the inner surface of the slagging chamber. The layer of molten slag contributes to protecting the walls of the slagging chamber from any high temperature flames that may be present in the slagging chamber. The slagging furnace may be constructed and operated such that substantially all, ie, at least 90% of the separated ash components are collected as a layer of molten slag in the slagging chamber. The proportion of ash component collected can be calculated from the mass balance by knowing the average ash content of the first fuel and the amount of slag withdrawn from the slagging chamber. Since most of the ash is collected in the slagging chamber, the ash is less likely to cause defects in the molten product.

In addition, the separated ash component released toward the melting furnace can promote deterioration of the refractory material of the melting furnace. Reducing the amount of the separated ash component entering the combustion space of the furnace can reduce corrosion of the refractory material of the furnace.

In addition, the separated ash component released toward the melting furnace can increase the mass flow rate of the solid particles discharged from the melting furnace. Therefore, by reducing the amount of the separated ash component entering the combustion space, it is possible to reduce the size of the particle control device required to clean the exhaust gas flow in the melting furnace.

The use of a second oxidant mixture and an optional second fuel can provide several advantages. Reinforcement of slag temperature control is one of the advantages of the method according to the present invention, because reinforcement of slag temperature control can increase the trapping of particles and improve the turndown of the process. The correlation between slag temperature and particle collection is established through the viscosity of the slag. Proper slag viscosity is required for the molten slag attached to the walls of the slagging chamber to efficiently capture the particles. Low slag temperatures cause the viscosity to become excessively high, causing local coagulation, resulting in the particles leaving the slag surface and returning to the gas phase. On the contrary, when slag temperature is high, a state with low viscosity will be formed and it will also become slag which tends to flow comparatively inadequate. The selective use of enriched oxygen and / or auxiliary fuels provides effective slag temperature control means that are not dependent on other process operating parameters.

The method of the present invention transfers the gas emissions of the slagging combustion furnace from the slagging chamber of the slagging combustion furnace to the combustion space 16 in the melting furnace 10 at a temperature of 1000 ° C to 2500 ° C to supply heat for forming the molten product. It includes a step. Hot combustion gases can be used to melt the raw material to provide heat to form the molten product.

The temperature can be measured using a suction pyrometer, an example of such a suction pyrometer is a water-cooled suction pyrometer probe available from METLAB, Enkoping, Sweden. Water-cooled suction pyrometer probes are also available from the International Flame Research Foundation (IFRF) in the Netherlands. Temperature measurements of furnace gases are known in the art. Any suitable device known in the art may be used to measure the temperature of the gaseous emissions to the slagging combustion furnace.

Gas emissions from slagging furnaces are usually non-luminescent gas media for supplying heat to the furnace. Luminescence can be described in terms of emission ratio. Luminescence ratio is defined herein as the ratio of thermal radiation in the 600 nm to 1500 nm band from a heating source to thermal radiation in the 600 nm to 4800 nm band from a heating source (see, eg, US Pat. No. 5,575,637). Non-luminous heating sources have luminous ratio values of 0.14 or less, while luminous heating sources have luminous ratios greater than 0.14. The luminescence ratio can be calculated from the spectral emission signal of the gas heating medium. Spectroradiometers such as Macam Spectroradiometer systems can be used to measure spectral emission data.

Luminescence of hot gases is obtained by blackbody radiation from particles contained in the gas. Such particles include two components, soot particles formed through nucleation of gaseous hydrocarbons during the fuel combustion process, and residual particles contained within the fuel source. However, the concentration of gaseous hydrocarbons produced by the process of the present invention is low because of the relatively large amount of combustion that occurs in the slagging chamber to maintain the temperature above the melting point of the ash. In addition, according to the method of the present invention, since the ash removal process is provided, the amount of residual fuel particles is small. Thus, the main heating mode in the melting chamber is convection from the gas emissions of the slagging combustion furnace to the melt / raw material and radiation from the walls and roof of the furnace to the melt / raw material.

Non-luminescent heating is contrary to the teachings of the prior art using coal or other finely divided solid fuels.

For example, in US Pat. No. 4,006,003 to Daiga, it is produced from a slurry of coal and oil comprising 27 wt% coal (73 wt% oil) and 40 wt% coal (60 wt% oil), respectively. The flames have been observed to have better luminescence than flames produced only from oil. In addition, Daiga's patent placed a burner approximately 2 ft above the level of the glass melt, with the flame tilted downward toward the surface of the pool of glass melt so that the tip of the flame floated on the pool of glass melt (not molten). The burner was adjusted to lick the upper surface of the ingredient.

U. S. Patent No. 3,969, 068 to Miller et al. Relates to a method and apparatus for burning coal directly in a glass tank furnace, in which a pulverized coal entrained in the air stream is forced through a nozzle into a furnace, It is combusted in an atmosphere directly above the molten product of to form a luminescent flame, and direct coal combustion is preferably used with conventional supplemental heat sources. The object of the '068 patent is to provide an improved novel method and apparatus for the direct combustion of coal in a glass tank furnace to provide a luminescent flame that heats the glass melt more effectively.

U.S. Patent No. 6,789,396 to Olin-Nunez et al. Discloses that while the furnace is operating, the regenerator alternates between one of the air combustion cycle and the exhaust cycle. Depending on the particular furnace, the flame path of the series of burners is switched every 20 or 30 minutes. Thus, the flame and combustion products finally formed at each burner pass across the surface of the glass melt and transfer heat to the glass in the melting chamber and the refining chamber.

U.S. Patent Application No. 2006/0150677, filed by Kobayashi, discloses that an oxygen-fuel burner is arranged to maintain a flame on the surface of the glass melt inside the furnace.

Optionally, the luminescence of the gaseous emissions of the slagging combustion furnace injects a third fuel into the combustion space of the melting furnace, mixes at least a portion of the third fuel with at least a portion of the gaseous emissions of the slagging combustion furnace, and It may be augmented by burning at least a portion of the third fuel in the combustion space to form a luminescent flame. The third fuel may be a fuel which contains little ash component, ie less than 0.1% by weight. The third fuel may be heavy oil, diesel, gasoline, kerosene, propane, methane, natural gas, or mixtures thereof. The composition of the third fuel may be the same as the composition of the second fuel.

The method includes the step of withdrawing molten slag 42 from the slagging chamber 12 of the slagging combustion furnace 14. If the molten slag is not compatible with the molten product, the molten slag is discarded. If the molten slag is compatible with the molten product, the molten slag may be controllably introduced into the melt / raw material space 18.

In the case of glass melting furnaces, molten slag is selectively introduced into the melting end or melting zone of the glass melting furnace and not into the clarification zone. The introduction of the molten slag into the melting zone of the glass furnace further provides an opportunity to homogenize the molten slag in the glass product in the glass furnace prior to the shaping operation of the glass.

The glass melting furnace can be divided into two zones, the melting zone and the clarification zone. The melting zone corresponds to the length in which the visible (visible) batch (unmelted raw material) in the glass melting furnace is present on the surface of the melt. Visible batches on the surface of the melt may be in the form of batch blanks, batch piles, batch islands, batch logs, and the like. The length of the melt zone extends from the rear wall to the visible placement that is located furthest downstream, and may comprise a zone of melt without visible placement on the surface of the glass melt. The clarification zone corresponds to the remaining length of the glass furnace. As described herein, the front wall corresponds to the furnace wall on the downstream side and the rear wall corresponds to the furnace wall on the upstream side. The size of the length corresponds to the overall flow of the glass melt moving from the rear wall to the front wall. The injection end corresponds to the end of the furnace into which the glassmaking raw material is introduced. The glassmaking raw material may be introduced into the furnace at the rear wall or at either or both of the sidewalls near the rear wall.

In glass melting furnaces, the process of the invention can be used in a variety of complex forms. The process of the invention results in at least 50% pure oxygen combustion in the melting zone and at least 50% air-fuel combustion in the clarification zone. The process of the present invention utilizes a slagging combustion furnace in the melting zone and may use conventional oxy-fuel burners and / or air-fuel burners in the clarification zone.

Pure oxygen combustion is defined herein as combustion in which the average oxygen concentration of the oxidant mixture is between 30 vol% and 100 vol% during combustion. Air-fuel combustion is defined herein as combustion in which the average oxygen concentration of the oxidant mixture is between 15 and 22 volume percent during combustion. Oxygen-rich air-fuel combustion is defined herein as combustion in which the average oxygen concentration of the oxidant mixture is from 22 to 30 volume percent during combustion. When a plurality of oxidant streams are introduced to combust the fuel, the determination of the combustion type is based on the volume flow rate weighted average of the plurality of oxidant streams.

As mentioned above, only a portion of the first fuel is combusted in the slagging combustion furnace, leaving unburned combustible gas available for combustion in the melting furnace 10. The method includes reacting only a portion of the first fuel to leave a substantial amount of at least one unburned combustible gas. In addition, the method further comprises introducing a third oxidant mixture into the combustion space 16 of the furnace 10. The third oxidant mixture may be introduced at a third oxidant mixture volume flow rate (V ₃ ).

The third oxidant mixture may have an oxygen concentration (Y ₃ ) of 20% to 100% by volume. The remainder of the third oxidant mixture may comprise nitrogen, carbon dioxide, water vapor, argon and traces of other species.

The third oxidant mixture may have an oxygen concentration of 60 vol% to 75 vol% or 85 vol% to 100 vol%. The tertiary oxidant mixture can be obtained from the exhaust stream of the nitrogen plant. The third oxidant mixture may be industrial grade oxygen produced in an air separation plant. The third oxidant mixture may come from the same source as the second oxidant mixture and may be of the same composition.

The method may comprise combusting at least a portion of the at least one unburned combustible gas obtained from the gaseous emissions of the slagging combustion furnace in the combustion space of the furnace with at least a portion of the third oxidant mixture.

The third oxidant mixture may be introduced between the gaseous emissions of the slagging combustion furnace and the melt / raw material space. The slagging furnace has at least one discharge port for discharging gaseous emissions of the slagging furnace. The nozzle for introducing the third oxidant mixture may be disposed between the melt / raw material space and the at least one discharge port for discharging gaseous emissions to the slagging combustion furnace.

The method of the present invention may further comprise introducing a slagging additive into the slagging chamber. Slagging additives may include glass cullets, one or more glassmaking raw materials, and / or ash from other processes.

If the ash content of the first fuel is very low, such as for example in petroleum coke or anthracite, it may be difficult to form a suitable layer of molten slag. The layer of molten slag serves as a barrier to protect the underlying substrate of the slagging chamber from high temperature damage. Another role of the additive is to remove contaminants from the fuel / ash mixture. Conventional calcium or magnesium based adsorbents are examples of adsorbents that can be used for this purpose. The slagging additive can be introduced to the slagging chamber in any suitable manner. The slagging additive may be introduced with the first fuel, with the second fuel, with the first oxidant mixture, with the second oxidant mixture, or in a separate flow.

Those skilled in the art will appreciate that selective use of oxygen can reduce NO _x emissions. For example, injecting oxygen near the first fuel nozzle where the first fuel is introduced into the slagging chamber will enhance the evaporation of the first fuel before complete mixing of the first fuel and the first oxidant mixture is achieved. Alternatively, the oxidant mixture may be introduced into the downstream section of the slagging chamber, causing staged combustion inside the slagging chamber. As described above in connection with the third oxidant mixture, the oxidant mixture may be introduced into the furnace, causing staged combustion in the furnace and outside of the slagging chamber.

When an optional second fuel is used, NO _x emissions have been observed to be affected by the equivalent ratio of the second fuel and the second oxidant mixture. A second fuel and second oxidant mixture having an equivalent ratio of 1.4 to 3 can be introduced. In general, the equivalent ratio is defined as the fuel: oxidant ratio divided by the fuel: oxidant ratio corresponding to complete combustion. The latter ratio (fuel: oxidant ratio corresponding to complete combustion) is usually referred to as the stoichiometric fuel: oxidant ratio. Equivalent ratio 1 means that the fuel and oxidant are provided in theoretically correct amounts or in stoichiometric amounts. Equivalence ratios greater than 1 correspond to fuel rich conditions, and equivalent ratios less than 1 correspond to fuel lean states.

FIG. 2 is a plot showing normalized NO _x emissions as a function of the equivalent ratio of the mixture of the second fuel and the second oxidant. In this experiment, the first oxidant mixture is air, the first fuel is bituminous coal, the second fuel is No. 2 heavy oil, and the second oxidant mixture is nearly 100% oxygen (obtained from the LOX source). The fuel energy input from the second fuel was 18% of the total energy. The total equivalent ratio of the combustion process, including all fuel and oxidant mixtures, was about 0.79. As can be seen in FIG. 2, the value of NO _x decreases by more than half while the second fuel and the second oxidant mixture are acting close to the stoichiometric action (ie, in an equivalent ratio of about 1). As the equivalence ratio is increased, the upper limit of the equivalence ratio is proposed to be about 3 since the effectiveness of the mixture of the second fuel and the second oxidizer to assist in the maintenance of the liquid slag layer is reduced.

Another potential advantage of using oxygen is the wider range of fuels that can heat the furnace. In addition, this advantage stems from the fact that the slag temperature can be independently controlled through the adjustment of either combustion of the second oxidant mixture / second fuel and selective oxygen concentration as described above. For example, combustion of coal with high ash melting points has traditionally been a problem in air-fuel fired slagging furnaces because they cannot generate temperatures high enough to maintain stable slag flow. The results of a test conducted by burning low sulfur coal with high ash melting point in a 2.5 MMBtu / h (0.73 MW heat) slagging furnace showed that slagging according to the method of the present invention in which No. 2 heavy oil participated in the combustion by 20%. And the overall performance operation is proved to be stable. In contrast, with air-fuel combustion alone, stable molten slag could not be maintained. Similar benefits can be obtained through other solid fuels that attempt to solve the problem of slag, including many coals, biofuels and the like with a high moisture content.

While particular embodiments of the present invention have been described in detail, those skilled in the art will understand that various modifications and changes may be made in light of the overall teachings herein. Thus, although the invention has been illustrated and described herein with reference to some specific embodiments and variations thereof, it is not intended to be limited to the details thus illustrated and described. Rather, various modifications may be made in the above detailed description within the scope and scope of the claims and without departing from the spirit of the invention.

1 is a schematic view of a melting furnace having a slagging combustion furnace;

2 shows a plot of NO _x emissions versus equivalent ratio of a mixture of a second fuel and a second oxidant.

<Explanation of symbols for the main parts of the drawings>

10: melting furnace

14: slagging combustion furnace

16: combustion space

18: melt / raw space

20: first fuel

22: first oxidant mixture

30: second fuel

32: second oxidant mixture

40 gas emissions from slagging furnaces

42: molten slag

Claims (17)

A method of supplying heat to a melting furnace to form a molten product, Introducing a first fuel having an ash component and a combustible component into the slagging chamber of the slagging combustion furnace; Introducing a first oxidant mixture having an oxygen concentration between 10% and 100% by volume into the slagging chamber of the slagging furnace; Selectively introducing a second fuel into the slagging chamber of the slagging combustion furnace; Introducing a second oxidant mixture having an oxygen concentration between 22% and 100% by volume into a slagging chamber of the slagging furnace; Combusting at least a portion of the combustible components of the first fuel and at least a portion of the optional second fuel in a slagging chamber of the slagging furnace to form a separate ash component and form a gaseous emission to the slagging furnace; Collecting at least a portion of the separated ash component as a layer of molten slag in contact with at least a portion of an inner surface of the slagging chamber; Transferring at least a portion of the gaseous emissions of the slagging combustion furnace from the slagging chamber of the slagging combustion furnace to a combustion space in the furnace at a temperature of 1000 ° C. to 2500 ° C. to supply heat to form the molten product; And Withdrawing molten slag from the slagging chamber of the slagging combustion furnace Heat supply method for the melting furnace comprising a. The method of claim 1, wherein the oxygen concentration of the first oxidant mixture is from 20 volume% to 30 volume%. The method of claim 1, wherein the oxygen concentration of the first oxidant mixture is 10 vol% to 20 vol%. The method of claim 1, wherein the oxygen concentration of the second oxidant mixture is from 60 vol% to 75 vol%. The method of claim 1, wherein the oxygen concentration of the second oxidant mixture is between 85 vol% and 100 vol%. The method of claim 1, wherein the gaseous emissions of the slagging combustion furnace contain at least one unburned combustible gas. 7. The method of claim 6, further comprising the steps of: introducing a third oxidant mixture having an oxygen concentration between 20% and 100% by volume into the combustion space of the furnace; And And combusting at least a portion of the at least one unburned combustible gas obtained from the gaseous emissions of the slagging furnace in the combustion space of the furnace with at least a portion of the third oxidant mixture. . 8. The method of claim 7, wherein the oxygen concentration of the third oxidant mixture is from 60 vol% to 75 vol%. 8. The method of claim 7, wherein the oxygen concentration of the third oxidant mixture is between 85% and 100% by volume. 8. The method of claim 7, wherein a third oxidant mixture is introduced between the gaseous emissions of the slagging combustion furnace and the melt / raw material space. The method of claim 1, further comprising introducing molten slag into the furnace. The heat supply to a melting furnace of claim 1, wherein the melting furnace is a glass melting furnace having a melting zone and a clarification zone, and further comprising introducing molten slag into the melting zone and not introducing it into the clarification zone. Way. The method of claim 1, further comprising introducing a slagging additive into the slagging chamber. The method of claim 13, wherein the slagging additive comprises at least one of glass cullets, glassmaking raw materials, or ash from other processes. The method of claim 1, wherein the first oxidant mixture contains flue gas exiting the furnace and the first oxidant mixture has an oxygen concentration of 10% to 20% by volume. The method of claim 1, wherein the second fuel contains at least a portion of the gaseous emissions of the slagging combustion furnace. The process of claim 1 wherein a mixture of a second fuel and a second oxidant having an equivalent ratio of 1.4 to 3 is introduced.

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